Rats and the City: The Urbanization of Mice's Genes and Appetite

A world full of this “Pizza Rat” in the video below? No. Way. Not my pizza!

But unfortunately, this is a possibility. Stephen Harris at the State University of New York and Jason Munshi-South of Fordham University examined 48 white-footed mice (Peromyscus leucopus) they caught in three New York parks and other three nearby rural areas to know whether some of these has been evolving to city life.

That is, they wanted to know whether there are certain difference on New York mice's genetic make-ups from their country cousins'. Specifically testing 19 single nucleotide polymorphisms (SNPs), they were able to look into mice's digestion and other metabolic processes. With this, they highlighted a gene used to produce omega-3 and omega-6 fatty acids.

Another noticeable gene is related to non-alcoholic fatty liver disease. Researchers said that this may be due to a fast food rich diet that resulted to the increased fatty acids needed to be processed. “The first thing that we thought of was the ‘cheeseburger hypothesis’: urban mice subsidising their diet on human food waste,” says Harris. Urban mice were even found to have larger livers with more scar tissue.

The work is “at the forefront of biology”, says Jonathan Richardson at Providence College in Rhode Island.

Whether fast foods caused this or not, though, still remains a question as New York also provides other foods, like seeds, nuts and berries for them to eat. And the fact that there are more resources and less competition in these areas adds up to this. Moreover, the study is also still limited to its small sample size.

So, a closer examination on these genes with regards to their impact on fitness and selection would be a great step forward, says Hopi Hoekstra at Harvard University. Nonetheless, the study “provides us with a really cool way to study evolutionary change, sort of as it’s happening,” she says.